Irradiation of exposure light is performed through a photomask (reticle), for example, to form a transfer pattern in a manufacture of the semiconductor device.
A photomask formed with a light-shading film pattern on a transparent substrate composed of a rectangular quartz glass is conventionally used, and as a material of a light-shading film, a chromium-based material (elementary chromium, or chromium containing nitrogen, oxygen, and carbon, etc, or a lamination film of these material films) is generally used.
Further, in recent years, a phase shift mask has been developed for practical use, to improve a resolution of the transfer pattern. Various types (for instance, a Levenson-type, an assist-pattern-type, and a self-matching type, etc) are known as the phase shift mask, and as one of them, a halftone phase shift mask suitable for the pattern transfer of a hole and a dot with high resolution is known.
This halftone type phase shift mask is obtained by forming a light translucent film pattern having a phase shift amount of about 180 deg, wherein the light translucent film is sometimes formed of a single layer or sometimes formed of multi-layers. For example, patent document 1 discloses the light translucent film pattern formed of a thin film composed of a substance containing metal such as molybdenum, silicon, and nitrogen as main constituent elements.
The light translucent film with such materials is excellent in acid resistance and resistance to light, in addition to having an advantage capable of controlling a prescribed phase shift amount and transmittance by a single layer.
When manufacturing these photomasks, it is necessary to form a fine pattern and therefore a pattern forming method of the photomask generally includes the steps of forming a resist pattern by exposing the resist to light by performing pattern drawing by an electron beam exposure apparatus; and thereafter forming the pattern by dry etching.
Note that as the kinds of the resist, there are a positive resist and a negative resist.
The positive resist is the resist having a property that a part irradiated with electron beam is removed by a resist developer, and the negative resist is the resist having a property that a part excluding the part irradiated with the electron beam is removed by the resist developer.
The choice as to which of the positive resist and the negative resist is used is made, to select more preferable one in terms of forming the pattern or shortening of drawing time of the electron beam exposure apparatus.
In addition, the aforementioned transfer pattern is formed in a rectangular main region located in a center portion of the rectangular transparent substrate, and during using the photomask, outer peripheral part of this main region is shield by a masking blind provided in the exposure apparatus, and the pattern of the main region is transferred to the resist on the transfer substrate.
In addition, in order to prevent the transfer to the outer peripheral part of this main region by leaked light, the photomask generally has a light shading band region adjacent to the main region.
In addition, in the photomask, a mark pattern, etc. of an alignment mark, etc, generally used for aligning with each kind of devices for photomask exists mainly in the peripheral part of the main region depending on specifications of each exposure apparatus manufacturer, a photomask user, and a photomask manufacturer.
Conventionally, when the pattern transferring is made using the positive resist, the peripheral region of the main region, excluding a desired mark pattern, is made, as a non-drawing region, where a light-shading film is formed.
On the other hand, when the pattern transferring is made with the negative resist, the peripheral region of the main region, excluding desired mark pattern and light-shading band, is made as, the non-drawing region, where the transparent substrate is exposed.
Namely, exposing patterns on the resist are performed by scanning a substrate surface based on pattern data.
Therefore, it is general to shorten a drawing time to avoid drawing, patterns on an unnecessary region.
Further, in order to prevent adhesion of foreign matters to the formed pattern, it is general to use the photomask by mounting a protective film called a pellicle.
The pellicle is formed by adhering a pellicle film consisting of a transparent polymer membrane to a pellicle frame usually consisting of metal, and this pellicle frame is attached to a surface of the photomask by using an adhesive.
More specifically, the pellicle frame is adhered to an outside of the light-shading band by using the adhesive, to cover the main region and the light-shading band.
In addition, in order to prevent the foreign matters from adhering onto the photomask, the adhesive is sometimes provided to an inner surface of the pellicle frame.
Note that the aforementioned each kind of mark pattern could exists not only in the pellicle but also outside the pellicle.
Incidentally, it is known that when the pattern transfer is performed by using the photomask, with pellicle mounted thereon, the pellicle is irradiated with laser beams, thereby accelerating reaction of ammonium ions that exist in the pellicle (in the air) and sulfate ions which are used for cleaning the photomask and are remained on the photomask, then, ammonium sulfate is deposited, and such the foreign matters are adhered onto the photomask (for example, patent document 1).    (Patent document 1) Japanese Patent Laid Open No. 2000-352812
However, in the photomask, with the transfer pattern formed thereon by using the negative resist, namely, the photomask, with the non-drawing region, namely the transparent substrate exposed in the peripheral region of the main region excluding the desired mark pattern and the light-shading band, there occurs a problem that a plurality of foreign matters are found in the photomask after use.
In addition, it is found that above problem is more remarkable in the photomask with the transfer pattern formed thereon by using the negative resist than in the photomask with the transfer pattern formed thereon by using the positive resist.
Accordingly, regarding the photomask with the transfer pattern formed thereon by using the negative resist, namely, the photomask, with the non-drawing region, namely, the transparent substrate exposed in the peripheral region of the main region excluding a desired mark pattern and the light-shading band, there is a problem that the photomask becomes unusable with a few using times.
As a cause of generating the aforementioned problem, there is given such a case that when the adhesive used for adhering the pellicle frame to the photomask is directly adhered to the transparent substrate, a stray light by a multiple reflection of the exposure light in the exposure apparatus during using the photomask transmits from a rear surface side of the transparent substrate to the transparent substrate, whereby the adhesive used for adhering the pellicle frame to the photomask, or the adhesive used for adhering the pellicle film to the pellicle frame, and further the adhesive inside of the pellicle frame if the adhesive is given thereto are irradiated with this stray light, and as a result, gas generated from the adhesive, being an organic substance, becomes a deposited substance, and would be adhered onto the photomask.
In addition, when the adhesive is not applied to the inside of the pellicle frame, it can be considered that components remained by an alumite treatment of the pellicle frame (including a coloring process) or the component remained by coating processing, etc, of the pellicle frame are deposited by irradiating the pellicle frame with the stray light which is caused by the multiple reflection, etc, of the exposure light in the exposure apparatus when using the photomask, and this stray light transmits the transparent substrate from the rear surface side to emit onto the pellicle frame, thereby adhering a deposit onto the photomask.
In addition, it is confirmed that the aforementioned problem becomes more remarkable, as a light source wavelength of the used exposure apparatus becomes shorter from the present KrF excimer laser (wavelength of 248 nm) to an ArF excimer laser (wavelength of 193 nm) and a F2 excimer laser (wavelength of 157 nm).
Therefore, there is a problem that even more foreign matters could be generated, as the exposure light wavelength applied by the exposure apparatus becomes shorter, accompanied by applying finer LSI pattern in recent years.
FIG. 5 shows an example of energy possessed by the light source wavelength of the exposure apparatus and a bonding energy of organic substances coming from matters such as the adhesive, etc.
In this way, as the wavelength of the light source of the exposure apparatus becomes shorter, it can be considered that the bonding energy possessed by molecules of the adhesive is more liable to be cut, and simultaneously a polymerization reaction or a radical reaction could occur, and as a result, generation of gas or generation of deposits become even remarkable.